The present invention relates to a drive wheel and a chassis for wheeled vehicles such as wheelchairs.
It has long been understood that wheels can assist in the transport of vehicles. However, vehicles having traditional wheels do suffer from a number of disadvantages that occasionally make such wheels unsuitable for particular applications. One instance where traditional wheels can present problems is on wheelchairs used for the transportation of temporarily or permanently disabled persons. Using traditional wheels, such wheelchairs can typically be quite cumbersome to operate and often cannot negotiate a twisting pathway that could, for example, be easily negotiated by a person on foot.
A number of wheels and wheeled assemblies have been developed that do allow vehicles, such as wheelchairs, to negotiate paths that would otherwise be not possible with traditional wheels. An example of one particular arrangement is described in International Publication Number WO 93/20791. This application describes a wheeled chassis having at least one driven wheel. The wheel is connected to the chassis by a steerable support that extends from the chassis perpendicularly to the ground over which the wheel is designed to travel. The wheel itself comprises a bearing block mounted to the steering support and a wheel member that is rotatable relatively to the bearing block. The wheel has a tread member extending about its periphery that is the portion of the wheel that contacts the surface while the wheel is travelling over the ground. The wheel described in this application is characterised in that where the tread of the wheel makes contact with the surface on which it is travelling, it is longitudinally aligned with the axis of the steerable support.
While being a suitable arrangement for many applications, corrective steering movements are often still required when the assembly is in the proximity of a physical obstacle, such as an item of furniture.
A further assembly is described in European Patent Specification EP 0 414 671 which comprises a driven wheel which is obliquely arranged with respect to a surface over which it is designed to travel and which has at its periphery a partial spherical tread surface. For propelling the vehicle, the assembly includes a first drive shaft about which is mounted concentrically a drive gear that is provided for steering the assembly. In the assembly, the rotation of the drive shaft is not directly transmitted to the wheel but instead is transmitted through a transmission arrangement formed by three gear wheels to a second drive shaft that is connected to the rim of the wheel. The tread of this wheel is also not longitudinally aligned with the axis of the drive gear for the steering assembly.
The present invention is directed to an alternative drive wheel and chassis assembly to those described above.
According to a first aspect, the present invention consists in a drive wheel for traveling on a surface comprising a support member, a wheel member and a drive shaft. The drive shaft has a drive device engaging a drive surface on the wheel member to rotatably drive the wheel member relative to the support member. The drive shaft has a longitudinal axis and the engagement of the drive device and drive surface define in vertical cross-section a line of engagement that is at an acute angle relative to the longitudinal axis. And, the wheel member has a surface contacting portion extending about its periphery and positioned such that it is intersected by the line of engagement substantially at where it contacts the surface.
The support member can have a substantially hemispherical outer surface with the wheel member rotatable about an axle extending normal to an inner surface of the hemispherical member. The wheel member can comprise a frusto-spherical portion extending between first and second surfaces, the first surface having a larger cross-sectional diameter than that of the second surface and also being the drive surface of the wheel member. The surface contacting portion can also extend about the periphery of the frusto-spherical portion adjacent the first surface. The surface contacting portion can be fabricated from an elastomeric material, such as polyurethane and can have a curved outer surface.
In one embodiment, the drive shaft can extend substantially normal to the surface over which the wheel is intended to travel and be rotated relative to its longitudinal axis by a driving device.
The drive device can comprise a gear member adjacent one end of the drive shaft having teeth disposed thereon that are adapted to engage with corresponding teeth on the first or drive surface of the wheel member.
In a preferred embodiment, the gear member can comprise a conical bevel pinion adapted to engage with the teeth on the wheel member. In cross-section, the line of engagement preferably is at an angle of between about 10xc2x0 and about 25xc2x0 to the longitudinal axis of the drive shaft.
In a further embodiment, the support member of the wheel can be mounted to a support shaft. The support shaft can be rotatable about its longitudinal axis with the rotation of the support shaft about its longitudinal axis being controlled by a steering device, such as a steering motor. In a preferred embodiment, the drive shaft can extend through the support shaft.
The steering device and driving device can constitute part of or be controlled by a control unit for the wheel.
As the surface contacting portion of the wheel according to the present invention is not aligned with the longitudinal axis of the support shaft, any steering correction of the drive wheel while the drive shaft is stationary does not result in the wheel twisting frictionally with respect to the ground. Rather, the surface contacting portion travels in the path of a small circle about the longitudinal axis of the drive shaft thereby keeping that axis stationary. This is an advantage of the present wheel as it serves to lessen wear on the surface, such as a carpet, on which the wheel is turning. It also substantially lessens the strain imposed on the torque capability of the steering device and so reduces the drain on any power source used for the assembly, such as batteries.
The wheel according to the present invention also has a number of advantages over the prior art described above, including:
(i) no intermediate gear wheel having an axle that is journalled in a support arm is required to reverse the rotation of the wheel relative to the drive shaft in order to correctly compensate for rotation of the steering drive gear;
(ii) the distance between the axis of the drive shaft and the surface contacting portion of the wheel is relatively small, thereby lessening the eccentric load on the mechanical support system of the assembly; and finally
(iii) the drive gear on the drive surface of the wheel member can have a diameter that is a significant proportion of the effective diameter of the wheel, thereby reducing the load on the drive device for any given drive force.
According to a second aspect, the present invention consists in a chassis having at least one drive wheel for traveling on a surface. The drive wheel comprises a support member, a wheel member and a drive shaft. The drive shaft has a drive device adapted to engage with a drive surface on the wheel member and thereby rotatably drive the wheel member relative to the support member. The drive shaft has a longitudinal axis and the engagement of the drive device and the drive surface define in vertical cross-section a line of engagement that is at an acute angle to the longitudinal axis. And, the wheel member has a surface contacting portion extending about its periphery and positioned such that it is intersected by the line of engagement substantially at where it contacts the surface.
Each support member in the second aspect also preferably has a substantially hemispherical outer surface with the wheel member being rotatable about an axle extending normal to an inner surface of the hemispherical member. Each wheel member also preferably comprises a frusto-spherical portion extending between first and second surfaces. The first surface has a larger cross-sectional diameter than the second surface and also is the drive surface of the wheel member. The surface contacting portion preferably extends about the periphery of the frusto-spherical portion adjacent the first surface. The surface contacting portion can be fabricated from an elastomeric material and have a curved outer surface.
In the chassis, the drive shaft of each driven wheel can be substantially normal to the surface over which the chassis is designed to travel. Each drive shaft can also be rotated relative to its longitudinal axis by a driving device.
In a preferred embodiment of the second aspect, each drive shaft of the drive wheels on the chassis extends through a corresponding one of the support shafts.
The drive device in the second aspect can comprise a gear member adjacent one end of the drive shaft having teeth disposed therein that are adapted to engage with corresponding teeth on the first or drive surface of the wheel member. In a preferred embodiment, the gear member can comprise a conical bevel pinion adapted to engage with the teeth on the first or drive surface of the wheel member. In cross-section, the line of engagement preferably is at an angle of between 10xc2x0 and 25xc2x0 relative to the vertical longitudinal axis of the drive shaft.
The support member for each driven wheel on the chassis can be mounted to a support shaft with the support shafts being preferably rotatable about their respective longitudinal axes. The rotation of each support shaft is preferably controlled by its own steering device.
The chassis according to the second aspect also preferably has a controlling device for controlling the operation of the steering device and the drive shaft. The controlling device can further include an operator-actuated device for controlling the movement of the chassis. In one embodiment, the operator-actuated device can comprise a joystick that allows the operator to control the movement of the chassis in a forwards and backwards direction, a sideways direction and also to turn the chassis as desired.
The motion of the chassis according to the second aspect of the present invention can be controlled by at least three signal transmitters, including:
an x-potentiometer for the longitudinal command;
a y-potentiometer for the sideways command; and
a xcfx89p-potentiometer for the ration command.
The at least three signal transmitters in this embodiment are preferably combined in a joystick.
In a further embodiment, the chassis can include a control system in which a correction factor is added to the signals received from the signal transmitters if the signals received from the signal transmitters result in the wheel velocity being less than a predetermined minimum velocity while the chassis velocity is greater than a predetermined maximum velocity so as to avoid instability in the chassis which would occur due to the wheel velocity suddenly shifting in direction.
The chassis according to the second aspect of the present invention is preferably for any wheeled vehicle adapted to carry a load. The wheeled vehicle can be selected from the group consisting of a wheelchair, patient hoist, shower chair, commode chair, transport chair, walking aid, fork lift, pallet mover, work table, robot, distribution trolley, mobile platform for camera and lighting equipment, luggage and shopping trolleys, hospital beds and cabinets, hospital waste containers, construction vehicles, earth moving vehicles, mining vehicles, and bomb disposal vehicles.
In a further aspect, the present invention comprises a chassis having at least two drive wheels, with at least one drive wheel being mounted on a first drive carriage and at least one drive wheel mounted on a second drive carriage of the chassis characterized in that the drive wheels on the respective first and second carriages can move relatively towards and away from each other.
In one embodiment of this further aspect, the drive carriages each have lateral members that telescopically or otherwise engage with respect to each other on movement of the drive wheels relatively towards and away from each other. The lateral members can telescopically or otherwise engage within a housing disposed between the drive wheels. In one embodiment, the housing remains midway between the drive wheels on movement of the drive wheels relatively towards and away from each other.
In a preferred embodiment of the further aspect, each drive wheel can comprise a drive wheel as defined herein as the first aspect of the present invention. In a further preferred embodiment, the chassis can comprise a chassis as defined herein as the second aspect of the present invention.